There are several reasons that ink-jet printing has become a popular way of recording images on various media surfaces, particularly paper. Some of these reasons include low printer noise, capability of high-speed recording, and multi-color recording. Additionally, these advantages can be obtained at a relatively low price to consumers. Though there has been great improvement in ink-jet printing, accompanying this improvement are increased demands by consumers in this area, e.g., higher speeds, higher resolution, full color image formation, increased stability, etc. As new ink-jet inks and print engines are developed, there have been several traditional characteristics to consider when evaluating the ink in conjunction with a printing surface or substrate. Such characteristics include edge acuity and optical density of the image on the surface, gloss, black to color bleed control, dry time of the ink on the substrate, adhesion to the substrate, lack of deviation in ink droplet placement, presence of all dots, resistance of the ink after drying to water and other solvents, long term storage stability, and long term reliability without pen material degradation or nozzle clogging. The long term reliability without material degradation or nozzle clogging becomes even more important with the advent of print engines that eject smaller drop volumes. Though the above list of characteristics provides a worthy goal to achieve, there are difficulties associated with satisfying all of the above characteristics. Often, the inclusion of an ink component meant to satisfy one of the above characteristics can prevent another characteristic from being met. Thus, most commercial inks for use in ink-jet printers represent a compromise in an attempt to achieve at least an adequate response in meeting all of the above listed requirements.
One characteristic of ink-jet printing systems that is desirable to achieve is related to frequency response of the ink-jet ink, which is often proportional to ink throughput. Smaller drop sizes have increased the demand for higher frequency printing. With respect to this aspect, obtaining increased printing speed while retaining acceptable print quality is a constant challenge in the ink-jet printing industry.
With respect to other aspects, improvement in black ink print quality, particularly with respect to optical density and bleed control, has been a consideration in the advancement of the ink-jet arts. Additionally, achieving acceptable optical density and bleed control in print reliable systems is also a consideration. For example, in one aspect, many ink-jet printing customers in the home printing market will often use a printer infrequently, or have lengthy breaks from use. Thus, some customers require reliable printing after long periods of down time, such as may occur as a result of a vacation or as a result of a summer break for students. As such, inks for such markets would benefit from formulations having long term storage stability in bottles, in print cartridges, and when loaded in a printer.
Accordingly, investigations continue into developing ink formulations that can be printed accurately at high frequencies, and which have good print quality and storage stability.